Photogrammetric system for positioning georadar data on the measurement scenario

ABSTRACT

A method for ground penetrating radar analysis of a scenario, having a surface, with respect to a cartesian reference system S(x, y) having origin O(0, 0) and axes x and y. The method comprises a step of prearranging a gpr apparatus that comprises at least one gpr sensor, a control unit, a centre of reference C(x c , y c ) having coordinates x c  and y c  with respect to the cartesian reference system S(x, y), at least one image acquisition devices, each image acquisition devices (110,120) having a pointing direction γ j  known with respect to the centre of reference C(x c , y c ). The method comprises then the steps of handling the gpr apparatus on the surface and detecting possible underground objects by means of gpr technique.

FIELD OF THE INVENTION

The present invention relates to the field of investigations using GPR(Ground Penetrating Radar) technique.

In particular, the invention relates to a method for assisting themovement and location of a GPR apparatus during the investigation of ascenario.

DESCRIPTION OF THE PRIOR ART

As known, the search for underground objects using GPR (GroundPenetrating Radar) technique finds many applications in the field ofcivil engineering, geology and archaeology.

The GPR devices provide at least one RF radio frequencyreceiver/emitting antenna (GPR sensor) and a remote control unitcomprising a PC and an interface card with the antenna. The GPR sensoris moved on the surface of the scenario to be investigated, and once thetransmission of the RF signal is initiated, the received feedbacksignals are generally displayed as bi-dimensional images.

To make a correct localization in the space of the detected objects, itis necessary to provide tools to help locating the GPR equipment, whenit detects an underground object, with respect to a known referencesystem. The main solutions used to derive the position of the GPRequipment in real-time space include, for example, the localization byGPS and/or by laser beam with respect to a local station of knownposition (total station).

However, these solutions are not always applicable. In particular, GPSlocalization is problematic in even partially covered places, whilelocalization by laser beam is impossible in the presence of objectsinterposed between the GPR equipment and the local station.

Moreover, both systems do not allow the operator to display in real timethe coordinates of objects visible in the scenario both in front of himand in planimetric view, an aspect that would greatly help a correctmovement of the GPR equipment and the interpretation of data collected.

US2017323480 discloses a system based on ground-penetrating radar (GPR)that visually depicts objects hidden by a surface. In particular, itprovides a realistic visualization of the hidden objects throughso-called augmented reality techniques. Thanks to such visualization,interaction with hidden objects is easier and less prone to errors. Thesystem can have two cameras in order to have a more realistic view ofthe environment.

However, US2017323480 does not provide in any way the possibility ofcreating a planimetry of the scenario that includes the GPR antenna,hidden objects and visible objects.

SUMMARY OF THE INVENTION

It is therefore a feature of the present invention to provide a methodfor ground penetrating radar analysis of a scenario that allows tolocate objects within the scenario with respect to the position assumedby the GPR apparatus and with respect to a predefined reference system,without needing to process information coming from other positioningsystems (eg GPS or local station).

This and other objects are achieved by a method for ground penetratingradar analysis of a scenario, having a surface, with respect to aCartesian reference system S(x,y) having origin O(0,0) and axes x and y,said method comprising the steps of:

-   -   prearranging a GPR apparatus, said GPR apparatus comprising:    -   at least one GPR sensor;    -   a control unit;    -   a centre of reference C(x_(c), y_(c)) having coordinates x_(c)        and y_(c) with respect to the Cartesian reference system S(x,y);    -   at least two image acquisition devices having respective        pointing directions γ₁ and γ₂ known with respect to the centre        of reference C(x_(c), y_(c));    -   handling the GPR apparatus on the surface;    -   detecting possible underground objects by means of GPR        technique;        whose main feature is that the step of handling comprises the        steps of:    -   acquiring at least two front images I_(F) of the scenario by        means of respective image acquisition devices, each image        comprising a plurality of pixels;    -   comparing the front images I_(F) for identifying pixel P_(i)        corresponding to a same point of the scenario;    -   localizing each pixel P_(i) of each front image I_(F) with        respect to both said pointing directions y_(i) and y₂, said step        of localization comprising a step of defining at least one        couple of angles ϑ_(xi) and ϑ_(yi) for each pixel P_(i);    -   processing, for each pixel P_(i), coordinates x_(i) and y_(i)        with respect to the Cartesian reference system

S(x,y);

-   -   reconstructing a plan image I_(p) of the scenario, said plan        image I_(p) comprising the plurality of pixels P_(i) arranged in        the coordinates x_(i) and y_(i).

Thanks to localization of the pixels in the scenario plan, it ispossible to know the dimensions and distance from the GPR equipment ofany object present above the surface of the scenario.

More specifically, a suitable software algorithm, using thecharacteristic parameters of the cameras, is able to determine thedistance, with respect to the GPR antenna, of an object framed by bothphotographic devices. This triangulation algorithm receives theinformation of the angle of observation for both cameras as input andreturns as a result the position (x,y) with respect to the centerbetween the two cameras, and therefore with respect to the GPR antenna.

To perform the triangulation must be known:

-   -   the “optical centre” of each camera, namely the exact position        in the 3D space of the sensor of the room on which the images        are impressed;    -   the “baseline” of the stereo-camera, namely the distance between        the two optical centres of the cameras;    -   the pointing angles in the 3D space of the two cameras with        respect to a reference centre, and therefore also the angles of        rotation of a camera relative to the other.

Moreover, to correctly perform the triangulation, one must also takeinto account the optical distortion parameters introduced by the cameralens, which must be appropriately compensated by the algorithm. Theseparameters are estimated through a particular calibration phase,together with the others previously mentioned parameters.

It should be noted that the cameras may have different viewing anglesand therefore do not necessarily have to point in the same direction inwhich the GPR is moved for scanning. However, it is necessary that partof the angle of view of both cameras is “superimposed”, in the sensethat at least part of the scene is framed by both the image acquisitiondevices in order to triangulate a given object, which must fall into theoverlapping area or, in other words, must be present in the frame ofboth cameras.

The triangulation algorithm is based on determining the point ofintersection between two lines in the three-dimensional space, whichpass through the optical centre of the respective camera and “meet” atthe point identified by the object. Knowing the distance between thecameras (baseline) we obtain the position in the 3D space of the object.The input information is given by the two pairs of pixels that indicatethe same object framed by the two cameras: each pixel is associated witha straight line in space, exiting from the optical centre of the system.

Since due to errors in the estimation of the parameters mentioned above,or to the resolution of the camera itself, it is possible that the twolines do not have a common intersection point, the algorithm determinesthe point in 3D space at minimum distance to which to associate theposition object. In the GPR technique this point is then projected ontothe survey surface, i.e. on a two-dimensional space, which indicates theposition (x, y) with respect to the GPR apparatus.

In this way, it is possible to have a plan of the scenario in whichvisible objects of the scenery and underground objects are virtuallysuperimposed in an advantageous manner with respect to the known art. Infact, in known technique this overlap is only possible using satellitemaps, which is not always available, especially in closed places. Thepresent invention, on the other hand, makes it possible to perform sucha planimetry, overlapping visible objects and underground objects, evenin the absence of GPS signal, also providing a planimetric image with amuch higher resolution than satellite images.

This plan allows to have more intuitive references for the localizationof underground objects, both to create simpler maps to be consulted andto facilitate the operator during the movement of the GPR equipment.

Advantageously, the GPR apparatus comprises a visual interface and astep is also provided of displaying the plan image I_(p) of the scenarioon the visual interface.

This way, the operator can display its own position in the scenario.

In particular, an iteration is provided, at time range t during the stepof handling, of the steps of:

-   -   acquiring at least one front image I_(F);    -   localizing each pixel P_(i);    -   processing, for each pixel P_(i), coordinates x_(i) and y_(i);    -   reconstructing a plan image I_(p) of the scenario.

This way, the position displayed within the scenario can be continuouslyupdated, even in real time.

Advantageously, also the front image I_(F) is displayed on the visualinterface.

In particular, on the visual interface, in superimposition to the frontimage I_(F) and to the plan image I_(P), graphic references aredisplayed for allowing defining a same point of the scenario on thefront image I_(F) and on the plan image I_(P).

This makes it possible to move the equipment easily even without visiblereferences in the scenario.

Advantageously, the GPR apparatus comprises a localization device whichis adapted to provide in real time to the control unit the coordinatesx_(c) and y_(c).

According to another aspect of the invention, it is claimed a method forground penetrating radar analysis of a scenario, having a surface, withrespect to a Cartesian reference system S(x,y) having origin O(0,0) andaxes x and y, said method comprising the steps of:

-   -   prearranging a GPR apparatus, said GPR apparatus comprising:    -   at least one GPR sensor;    -   a control unit;    -   a centre of reference C(x_(c), y_(c)) having coordinates x_(c)        and y_(c) with respect to said Cartesian reference system        S(x,y);    -   at least one image acquisition device, each image acquisition        device having a pointing direction γ_(j) known with respect to        the centre of reference C(x_(c), y_(c));    -   handling the GPR apparatus on the surface;    -   detecting possible underground objects by means of GPR        technique;        whose main feature is that the step of handling comprises the        steps of:    -   acquiring at least one front image I_(F) of the scenario, each        image comprising a plurality of pixels P_(i);    -   localizing each pixel P_(i) of the or each front image I_(F)        with respect to the or each pointing direction γ_(j), the step        of localization comprising a step of defining at least one        couple of angles ϑ_(xi) and ϑ_(yi) for each pixel P_(i);    -   processing, for each pixel P_(i), coordinates x_(i) and y_(i)        with respect to said Cartesian reference system S(x,y);

reconstructing a plan image I_(p) of the scenario, said plan image I_(p)comprising the plurality of pixels P_(i) in the coordinates x_(i) andy_(i).

Advantageously, steps are provided of:

-   -   arrangement within the scenario of a marker of known size;    -   acquisition by the or each image acquisition device of at least        one front image I_(F) comprising the marker;    -   calculating by means of the control unit the distance between        the marker and the or each image acquisition device.

Alternatively, the GPR apparatus comprises at least one angular positiontransducer, or encoder, able to detect changes in angular position ofthe or each image acquisition device.

Alternatively, a step of acquisition of the angular position of the oreach image acquisition device with respect to said scenario is provided.

Using one of the systems mentioned above, it is possible to realize theplanimetry of the scenario with a single camera. It is in fact possibleto obtain the position information from a series of images taken duringthe acquisition, even in real time.

In fact, the prior art does not allow to obtain the 3D positioninformation of the framed objects (or consequently the GPR coordinateswith respect to them) from the images, since it is necessary to obtain a“scale factor”. In general, the orientation (in the sense of rotationangles) in the 3D space of the camera relative to its previous positioncan be derived from the correlation between one image and the next one.The relative position is instead estimated up to a metric factorobtainable by means of a marker, an encoder or the knowledge of theangular position of the camera, as mentioned above.

Once the position of the GPR is known, with respect to a local referencecentre, in each acquired frame it is possible to carry out a reverseimage transformation to obtain a high resolution cartographic image. Forthis technique an algorithm is needed that, by interpreting the acquiredimages, recognizes the objects framed on multiple frames and fromdifferent viewing angles.

In particular, the GPR apparatus comprises at least two imagesacquisition devices having respective pointing directions γ₁ and γ₂known with respect to the centre of reference C(x_(c), y_(c)).

Advantageously, the step of acquisition provides the acquisition of twofront images I_(F) by means of respective images acquisition devices,each front image I_(F) comprising a plurality of pixels P_(i), andwherein the step of localization provides the localization of each pixelP_(i) of each front images I_(F) and the definition of a couple ofangles ϑ_(xi) and ϑ_(yi) for each pixel P.

In particular, they are also provided the steps of:

-   -   comparing the front images I_(F) for identifying pixel P_(i)        corresponding to a same point of the scenario;    -   localization of each pixel Pi with respect to both the pointing        directions γ₁ and γ₂.

In this way, there is a three-dimensional localization of the pixels,and therefore a more precise reconstruction of the scenario. Inparticular, the three-dimensional localization of pixels makes itpossible to more accurately calculate the dimensions and relativedistances of objects visible in the scenario.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristic and/or advantages of the present invention aremore bright with the following description of an exemplary embodimentthereof, exemplifying but not limitative, with reference to the attacheddrawings in which:

FIG. 1 shows a flow chart of the method, according to the presentinvention, wherein a single image acquisition device is provided;

FIG. 2 shows a flow chart of implementation variant of the method,according to the present invention, wherein two images acquisitiondevices are provided;

FIG. 3A shows a front image of the scenario;

FIG. 3B shows a plan image of the scenario.

DESCRIPTION OF A PREFERRED EXEMPLARY EMBODIMENT

The flow chart 300 of FIG. 1 shows the steps of a first variant of themethod for ground penetrating radar analysis in a scenario, according tothe present invention, wherein a single image acquisition device 110 isprovided, in particular a video camera or a camera.

The method provides a first step of prearranging a GPR apparatus with acamera on board [310], a second step of handling the apparatus on thesurface of the scenario to be investigated [320] and a third step ofdetecting possible underground objects [330].

With reference even at FIGS. 3A and 3B, the method according to thepresent invention provides that, during the step of handling theapparatus 100, there are some steps arranged to allow the operator tolocate, even in real time, the apparatus 100 and to display objects ofthe scenario 200 in a plan image of the scenario itself, in order tovirtually superimpose such objects of the scenario 200 to the detectedunderground objects.

In particular, there is a step of acquiring by the camera 110 a frontimage I_(F) [321], of which a schematic example is shown in FIG. 3A.

Then, by knowing the pointing direction γ₁ of the camera 110 withrespect to the centre of reference C(x_(c)y_(c)) of the apparatus 100,there is a step of localizing each pixel P_(i) of the image acquired, interms of angles ϑ_(xi) and ϑ_(yi) with respect to the pointing directionγ₁ [322].

Once localized the pixel P_(i) with respect to the position of theapparatus 100, it is possible, by transformation of coordinates, toprocess the x_(i) and y_(i) coordinates of each pixel P_(i) with respectto a Cartesian reference system S(x,y) of known origin and orientation[323].

Finally, by combining all the pixel with respect to their coordinates inthe reference system S(x,y), it is possible to reconstruct a plan imageI_(p) of the scenario 200, in order to provide an operator with a topplan view of its own position with respect both to possible undergroundobjects detected, both with respect to objects present in the scenarioabove the surface 200 [324].

The above described steps are then iterated at predetermined time rangesin such a way that the plan image I_(p) is updated periodically.

In a variant of the method, schematically shown by the diagram 300′ ofFIG. 2, two cameras 110 and 120 are provided having respective pointingdirections γ₁ and γ₂.

In this case, there are two front images I_(F) obtained and there is anadditional step of comparing the front images in order to identify thepixel P_(i) corresponding to a same point of the scenario 200 [325′].

This way, there is a three-dimensional localization of each pixel, bythe acquisition of two couples of angles, and so there is a more precisereconstruction of the scenario.

The foregoing description some exemplary specific embodiments will sofully reveal the invention according to the conceptual point of view, sothat others, by applying current knowledge, will be able to modifyand/or adapt in various applications the specific exemplary embodimentswithout further research and without parting from the invention, and,accordingly, it is meant that such adaptations and modifications willhave to be considered as equivalent to the specific embodiments. Themeans and the materials to realise the different functions describedherein could have a different nature without, for this reason, departingfrom the field of the invention. it is to be understood that thephraseology or terminology that is employed herein is for the purpose ofdescription and not of limitation.

1. A method for ground penetrating radar analysis of a scenario, havinga surface, with respect to a Cartesian reference system S(x, y) havingorigin O(0,0) and axes x and y, said method comprising the steps of:prearranging a GPR apparatus, said GPR apparatus comprising: at leastone GPR sensor; a control unit; a centre of reference C(x_(c), y_(c))having coordinates x_(c) and y_(c) with respect to said Cartesianreference system S(x, y); at least two image acquisition devices havingrespective pointing directions γ₁ and γ₂ known with respect to saidcentre of reference C(x_(c), y_(c)); handling said GPR apparatus on saidsurface; detecting possible underground objects by means of GPRtechnique; said method characterized in that said step of handlingcomprises the steps of: acquiring at least two front images I_(F) ofsaid scenario by means of respective image acquisition devices, eachfront image comprising a plurality of pixels; comparing said frontimages I_(F) for identifying pixel P_(i) corresponding to a same pointof said scenario; localizing each pixel P_(i) of each front image I_(F)with respect to both said pointing directions γ₁ and γ₂, said step oflocalization comprising a step of defining at least one couple of anglesϑ_(xi) and ϑ_(yi) for each pixel P_(i); processing, for each pixelP_(i), coordinates x_(i) and y_(i) with respect to said Cartesianreference system S(x, y); reconstructing a plan image I_(p) of saidscenario, said plan image I_(p) comprising said plurality of pixelsP_(i) in said coordinates x_(i) and y_(i).
 2. The method for groundpenetrating radar analysis, according to claim 1, wherein said GPRapparatus comprises a visual interface and where a step is also providedof displaying said plan image I_(p) of said scenario on said visualinterface.
 3. The method for ground penetrating radar analysis,according to claim 1, wherein, at time ranges t during said step ofhandling, it is provided an iteration of said steps of: acquiring atleast one front image I_(F); localizing each pixel P_(i); processing,for each pixel P_(i), coordinates x_(i) and y_(i); reconstructing a planimage I_(p) of said scenario.
 4. The method for ground penetrating radaranalysis, according to claim 2, wherein also said front image I_(F) isdisplayed on said visual interface.
 5. The method for ground penetratingradar analysis, according to claim 4, wherein, on said visual interface,in superimposition to said front image I_(F) and to said plan imageI_(P), graphic references are displayed for allowing defining a samepoint of said scenario on said front image I_(F) and on said plan imageI_(P).
 6. The method for ground penetrating radar analysis, according toclaim 1, wherein said GPR apparatus comprises a localization devicewhich is adapted to provide in real time to said control unit saidcoordinates x_(c) and y_(c).
 7. A method for ground penetrating radaranalysis of a scenario, having a surface, with respect to a Cartesianreference system S(x, y) having origin O(0,0) and axes x and y, saidmethod comprising the steps of: prearranging a GPR apparatus, said GPRapparatus comprising: at least one GPR sensor; a control unit; a centreof reference C(x_(c), y_(c)) having coordinates x_(c) and y_(c) withrespect to said Cartesian reference system S(x, y); at least one imageacquisition device, each image acquisition device having a pointingdirection y_(i) known with respect to said centre of reference C(x_(c),y_(c)); handling said GPR apparatus on said surface; detecting possibleunderground objects by means of GPR technique; said method characterizedin that said step of handling comprises the steps of: acquiring at leastone front image I_(F) of said scenario, each image comprising aplurality of pixels P_(i); localizing each pixel P_(i) of said or eachfront image I_(F) with respect to said or each pointing direction γ_(j),said step of localization comprising a step of defining at least onecouple of angles ϑ_(xi) and ϑ_(yi) for each pixel P_(i); processing, foreach pixel P_(i), coordinates x_(i) and y_(i) with respect to saidCartesian reference system S(x, y); reconstructing a plan image I_(p) ofsaid scenario, said plan image I_(p) comprising said plurality of pixelsP_(i) in said coordinates x_(i) and y_(i).
 8. The method for groundpenetrating radar analysis, according to claim 7, wherein steps areprovided of: arrangement within said scenario of a marker of known size;acquisition by said or each image acquisition device of at least onefront image I_(F) comprising said marker; calculating by means of saidcontrol unit the distance between said marker and said or each imageacquisition device.
 9. The method for ground penetrating radar analysis,according to claim 7, wherein said GPR apparatus comprises at least oneangular position transducer, or encoder, able to detect changes inangular position of said or each image acquisition device.
 10. Themethod for ground penetrating radar analysis, according to claim 7,wherein a step of acquisition of the angular position of said or eachimage acquisition device with respect to said scenario is provided. 11.The method for ground penetrating radar analysis, according to claim 7,wherein said GPR apparatus comprises at least two images acquisitiondevices having respective pointing directions γ₁ and γ₂ known withrespect to said centre of reference C(x_(c), y_(c)).
 12. The method forground penetrating radar analysis, according to claim 11, wherein saidstep of acquisition provides the acquisition of two front images I_(F)by means of respective images acquisition devices, each front imageI_(F) comprising a plurality of pixels P_(i), and wherein said step oflocalization provides the localization of each pixel P_(i) of each ofsaid front images I_(F) and the definition of a couple of angles ϑ_(xi)and ϑ_(yi) for each pixel P.
 13. The method for ground penetrating radaranalysis, according to claim 12, wherein are also provided the steps of:comparing said front images I_(F) for identifying pixel P_(i)corresponding to a same point of said scenario; localizing each pixelP_(i) with respect to both said pointing directions γ₁ and γ₂.